Crikey probably not, unless there is a version of DD_WRT he can use that supports his router
Edit: Although, he could wire the router into his existing network, means having a long ethernet wire though dpeending where he wants to extend it to. Then he'd essentially have 2 different wifi networks accessing the same internet connection
No he wouldn't have 2 different wifi networks.
If you make the two access points with the same exact ssid (using the same upper and lower case lettering, punctuation, etc) and the same security settings and access codes, then the wirless nic will seemlessly go about both "networks" attaching to the point with the strongest signal without a drop or connecting to a different access point. This has been in place since b standard and a standard.
You would need dd-wrt. but really with the cost of a new router (I saw a G router in wally world for 30 bux the other night after I bricked my wrt54g and needed a new one at 11pm) get a new router.
here is a e1000n for $22 http://www.amazon.co...15142132&sr=1-5
They are out there and they aren't that expensive. besides you will have more throughput on the newer routers that can cater to newer high speed internet access where that one tops out at maybe 3mb/s eventhough it is a 10mb port.